xii THE COLOURS OF ANIMALS 



kindly helped me in explaining the physical questions 

 involved in the first chapter. I am especially pleased 

 to speak of the help received from my former pupils 

 Mr. W. Garstangand Mr. E. C. L. Perkins, who have 

 supplied many valuable instances, which are specified 

 in the volume, where other kind assistance is also duly 

 acknowledged. 



Although I have ventured to disagree with my 

 friend Dr. A. R. Wallace upon the subject of ' Sexual 

 Selection,' I wish to acknowledge how very much I 

 owe to his writings, which I have very frequently 

 quoted. I have also made great use of the late 

 Thomas Belt's extremely interesting and suggestive 

 ' Naturalist in Nicaragua.' 



Among recent papers I wish especially to mention 

 that by G. W. and E. G. Peckham, of Milwaukee, 

 U.S.A. The minute observation of these authors 

 upon the courtship of spiders of the family Attidce is 

 a model for investigation in a subject which has never 

 before been attacked systematically. 



Above all, I should wish to acknowledge, although 

 I can never fully express, the depth of my indebted- 

 ness to the principles which first made Biology a 

 science, the principles enunciated by Charles Darwin. 

 It is common enough nowadays to hear of new 

 hypotheses which are believed (by their inventors) to 

 explain the fact of evolution. These hypotheses are 

 as destructive of one another as they are supposed to 

 be of Natural Selection, which remains as the one 



